Combining cognitive radio technology with user cooperation could be
advantageous to both primary and secondary transmissions. In this paper, we
propose a first relaying scheme for cognitive radio networks (called "Adaptive
relaying scheme 1"), where one relay node can assist the primary or the
secondary transmission with the objective of improving the outage probability
of the secondary transmission with respect to a primary outage probability
threshold. Upper bound expressions of the secondary outage probability using
the proposed scheme are derived over Rayleigh fading channels.